1. Technical Field
The present invention relates to a light-curable ink composition for ink jet recording and an ink jet recording method using this ink composition.
2. Related Art
To be of high quality and excellent color reproduction, color images formed by the ink jet process or similar processes should have optical properties such as a hue, transparency, and tinting strength and durability including weather resistance, heat resistance, and solvent resistance. They should also be safe. Pigments are more durable than dyes and thus in many cases are advantageous coloring materials over dyes for use in compositions for the formation of color images.
Yellow is one of the primary colors (yellow, magenta, and cyan), and widely used yellow pigments include Color Index (hereinafter abbreviated to C.I.) Pigment Yellow (hereinafter also referred to as PY) 74, 128, and so forth. These yellow pigments have room for improvement because the yellow colors they produce lack weather resistance.
To solve this problem, researchers have proposed many compositions, in particular, inks, that can produce yellow images that satisfies all of the above listed requirements.
For example, JP-A-2010-260281 discloses two ink compositions. One contains a liquid dispersion based on Pigment Yellow 155 and further contains an alicyclic epoxy compound, another epoxy compound, an oxetane, a cationic polymerizable compound (named Illustrative Compound 1-H in the publication), a surfactant, a photoacid generator, and an anthracene derivative, and the other contains a liquid dispersion based on Pigment Yellow 213 and further contains an alicyclic epoxy compound, another epoxy compound, an oxetane, a cationic polymerizable compound (Illustrative Compound 1-G), a surfactant, a photoacid generator, and an anthracene derivative (Ink Nos. Y-6 and Y-7 in Table 2).
JP-A-2009-1691 discloses an oily ink composition for ink jet recording. This composition contains a liquid pigment dispersion based on (1) C.I. Pigment Yellow 213, (2) C.I. Pigment Yellow 213 and 110, or (3) C.I. Pigment Yellow 213 and 139 and further contains diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, γ-butyrolactone, and an acrylic resin as a binder (Examples 1 to 3 of the publication, paragraphs [0042] to [0045]).
JP-T-2011-500932 discloses a yellow curable ink. This ink contains 3% by weight of C.I. PY 150 as an yellow pigment, 60.35% by weight of 2-(vinyloxyethoxy)ethyl acrylate (VEEA), and 2.5% by weight of a polymerization initiator (paragraphs [0405] to [0409] of the publication).
JP-A-2009-57548 discloses a light-curable ink composition. This composition contains 74.8% by weight of VEEA, 10% by weight of a hyperbranched polymer, 8% by weight of a polymerization initiator, and 7.2% by weight of a dispersion containing Pigment Yellow 155 (Example 4 in Table 1 of the publication).
These are all disadvantageous. The ink compositions according to JP-A-2010-260281 are difficult to cure with long-wavelength (350 to 420 nm) light-emitting diodes (LEDs) in an ultraviolet curing process using the photoacid generator and thus lack curability and become seriously viscous during that process. Worse yet, these ink compositions have unsatisfactory storage stability in some cases. The oily ink composition for ink jet recording according to JP-A-2009-1691 requires heating after printing because of its oily nature. During the heating process, some ingredients are evaporated and form VOCs (volatile organic compounds), which are impurities inherent to oily inks (inks based on organic solvent), and the ink composition itself becomes seriously viscous. The yellow curable ink according to JP-T-2011-500932 has room for improvement in safety because the pigment C.I. PY 150 contains nickel, and records produced using this ink are of unsatisfactory wet weather resistance (waterproofness). The light-curable ink composition according to JP-A-2009-57548 has room for improvement in storage stability.